The subject matter of the present invention pertains to pumps for use in oil well boreholes, and more particularly, to a pump apparatus which includes a firing head for use with a perforating gun on a tubing string adapted to be disposed in such borehole.
Perforating guns, run into a borehole on a tubing string, function to perforate a formation around a borehole of an oil well for the purpose of withdrawing well fluids from the formation. Very often, the well fluids do not produce from the formation with sufficient pressure to propagate up the borehole to the well surface. As a result, a pump is installed in the tubing string for pumping the well fluids to the surface. The perforating gun with its firing head is first run into the borehole on the tubing string. When the perforating gun, with its firing head, is in place within the borehole, the pump is installed, within the tubing string, just above the perforating gun. The firing head of the gun detonates a set of charges in the gun, perforating the formation. The well fluids produce from the formation and the pump functions to pump the well fluids to the surface. However, if the firing head malfunctions and fails to detonate the charges, since the firing head is run into the borehole on the tubing string, the pump must first be withdrawn from the borehole, and the tubing string must secondly be withdrawn from the borehole in order to replace the firing head. A work over rig must be used to withdraw the pump and to withdraw the tubing string. This repair process takes several days to complete. Increased repair costs result. In addition, the firing head includes primary explosives. Since the tubing string includes the perforating gun with the firing head, in view of the primary explosives present in the firing head, for safety reasons, it is necessary to handle with care the placement of the perforating gun into the borehole. Therefore, a new design is needed which will allow for the repair and replacement of a firing head of a perforating gun without simultaneously requiring the withdrawal of the entire tubing string from a borehole, a repair which normally takes several days to complete.